Have you tried simply contacting the museum? The Boston MFA site invites you to do this:

"If you have any questions about a particular artwork from the European collection, whether or not you can find a record for it online, please send an e-mail to webmaster@mfa.org. If you have a particular question or concern regarding the provenance (history of ownership) of a work from the European art collection, please send an e-mail to provenance@mfa.org or visit the MFA's WWII Provenance Research Project Web site."

Good luck!